The present invention relates to a vehicle seat including a side airbag effective for protecting a passenger on a vehicle such as an automobile, when the vehicle receives side impact.
An airbag apparatus mounted on a vehicle, such as an automobile, is an apparatus which instantaneously inflates an airbag by means of an inflator in case of collision, to protect a passenger by preventing him or her from second collision with an interior member of the vehicle. To protect the passenger from head-on collision, an airbag is amounted in front of the passenger, i.e., in the center pad of the steering wheel, or near the glove box in front of the assistant driver's seat. A so-called side airbag, incorporated in a seat back or the like, is effective for side impact.
FIGS. 7 and 8 shows a side airbag apparatus 1 provided in a conventional vehicle seat 2. The vehicle seat 2. incorporates an inflator 5 in a side portion 4 of a seat back 3 on the side nearer to a door. The inflator 5 is operated in response to a signal output from a sensor when the vehicle receives side impact, so that the airbag 6 is inflated by gas generated by the inflator 5. As shown in FIG. 8, the seat back 3 includes a frame 7, a pad 8, a cover member 9, etc. As the airbag 6 is inflated, a sewing thread 11 of a sewing portion 10 between a seat-back front cover element 9a and a side cover element 9b is cut by pressure developed inside and applied to the cover member 9. Then, the airbag 6 expands forward from the seat back 3 through the cut portion, as indicated by the two-dots-chain line B, and expands to a shape which can protect side and head portions of the passenger.
In the conventional seat back 3, the cover member 9 covering the pad 8 is made of artificial leather such as vinyl leather, or cloth such as woven fabric or knit fabric. The cover member 9 is manufactured as follows. First, rolled material 15A (a roll of a long sheet-like material 15) as shown in FIG. 9 is cut into shapes of the cover elements: the seat back front cover element 9a, the side cover element 9b, etc. Then, the cover elements are sewn together. According to the knitting structure of jersey, etc., constituting the lining fabric of the material 15 made of artificial leather or the like, the material 15 extends less in the longitudinal direction of the rolled material 15A (hereinafter referred to as the length direction, indicated by the arrow L) than in the lateral direction thereof (the width direction, indicated by the arrow W). For example, when the material is cut, the elongation percentage in the length direction L is 40 to 45%, while that in the width direction W is 230 to 240%.
To manufacture the cover member 9 of the conventional seat back 3 shown in FIG. 7, the seat-back front cover element 9a and the side cover element 9b are cut out from the rolled material 15A, such that the longitudinal directions of the elements 9a and 9b correspond to the length direction L of the material 15, as shown in FIG. 9. Therefore, the seat-back front cover element 9a and the side cover element 9b, after sewn together, extend less in the vertical direction of the seat back 3 than in the width direction and the back-forth direction thereof.
In the case where the cover member 9 extends less in the vertical direction than in the width direction and the back-forth direction thereof as in the conventional seat back 3 described above, when the airbag 6 is expanding forward as indicated by the two-dots-chain line B in FIG. 8, the cover member 9 tends to expand in the width direction of the seat back 3 as indicated by the dot-chain line C. For this reason, the force for cutting the sewing thread 11 of the sewing portion 10 between the seat-back front cover element 9a and the side cover element 9b may not be fully exerted on the sewing thread 11. In this case, a portion other than the sewing portion 10, for example, a portion of the side cover element 9b may be torn and the airbag 6 may be expands from that portion, resulting in a low inflating property of the airbag 9.